﻿crick: 
  on 
  ammonites 
  AMr7CrL.4i?75, 
  mantell. 
  155 
  

  

  originally 
  they 
  were 
  narrowly 
  rounded 
  and 
  of 
  the 
  same 
  width 
  as, 
  or 
  

   even 
  a 
  little 
  narrower 
  than, 
  the 
  interveninji 
  spaces 
  ; 
  the 
  ribs 
  are 
  

   straight, 
  and 
  as 
  a 
  rule 
  alternately 
  longer 
  and 
  shorter, 
  but 
  towards 
  

   the 
  anterior 
  end 
  of 
  the 
  specimen 
  there 
  are 
  irregularities 
  in 
  this 
  

   respect. 
  As 
  a 
  rule 
  each 
  longer 
  rib 
  commences 
  at 
  the 
  suture 
  of 
  the 
  

   shell 
  and, 
  increasing 
  in 
  strengtli 
  as 
  it 
  passes 
  across 
  the 
  inner 
  area 
  of 
  

   the 
  whorl, 
  is 
  raised 
  into 
  a 
  more 
  or 
  less 
  prominent 
  compressed 
  

   tubercle 
  on 
  the 
  umbilical 
  margin, 
  whence 
  the 
  rib 
  passes 
  stiaight 
  

   across 
  the 
  broadly-rounded 
  whorls 
  without 
  any 
  indications 
  of 
  

   tubercles. 
  In 
  one 
  instance 
  one 
  of 
  the 
  longer 
  ribs 
  bifurcates 
  at 
  the 
  

   tubercle 
  on 
  the 
  umbilical 
  margin, 
  the 
  two 
  divisions 
  being 
  continued 
  

   thence 
  across 
  the 
  whorl. 
  The 
  earliest 
  part 
  — 
  about 
  tlie 
  first 
  thiid 
  — 
  

   of 
  the 
  outer 
  whorl 
  is 
  A-ery 
  imperfect, 
  nearly 
  one-half 
  of 
  tlie 
  whorl 
  

   being 
  broken 
  awa\-, 
  but 
  even 
  here, 
  so 
  far 
  as 
  one 
  can 
  see, 
  there 
  are 
  no 
  

   traces 
  of 
  a 
  row 
  of 
  tubercles 
  on 
  each 
  margin 
  of 
  the 
  periphery. 
  

  

  The 
  imperfection 
  of 
  the 
  earliest 
  })ortion 
  of 
  the 
  outer 
  whorl 
  is 
  not 
  

   clearly 
  shown 
  in 
  Mantell's 
  figure, 
  which, 
  therefore, 
  causes 
  the 
  shell 
  

   to 
  appear 
  to 
  expand 
  much 
  more 
  rapidly 
  than 
  it 
  actually 
  does. 
  

   Unfortunately 
  the 
  [septal] 
  sutures 
  are 
  not 
  visible. 
  

  

  Respecting 
  the 
  pit 
  at 
  Offhara, 
  where 
  the 
  specimen 
  was 
  found, 
  

   Mantell 
  writes 
  (op. 
  cit., 
  p. 
  100) 
  : 
  " 
  This 
  excavation 
  lies 
  on 
  the 
  road- 
  

   side, 
  between 
  Offhara 
  and 
  Cooksbridge 
  ; 
  it 
  produces 
  anuno7iites, 
  

   nautili, 
  turrilites, 
  scaphites, 
  etc." 
  

  

  Tlie 
  road 
  from 
  Ofi^ham 
  (If 
  miles 
  north-west 
  of 
  Lewes 
  in 
  Sussex) 
  to 
  

   Cooksbridge, 
  about 
  a 
  mile 
  distant, 
  passes 
  almost 
  due 
  north 
  from 
  

   Offham, 
  and, 
  according 
  to 
  the 
  map 
  of 
  the 
  Geological 
  Survey, 
  the 
  

   portion 
  of 
  the 
  Chalk 
  traversed 
  by 
  it 
  is 
  referred 
  to 
  the 
  Lower 
  Chalk 
  

   only.' 
  In 
  neither 
  of 
  the 
  two 
  volumes 
  of 
  the 
  Memoirs 
  of 
  the 
  

   Geological 
  Survey 
  on 
  the 
  Cretaceous 
  llocks 
  of 
  Britain, 
  dealing 
  with 
  

   the 
  Lower 
  and 
  Middle 
  Chalk 
  (vol. 
  ii, 
  1903) 
  and 
  with 
  the 
  Upper 
  

   Chalk 
  (vol. 
  iii, 
  1904) 
  respectively, 
  is 
  there 
  any 
  reference 
  to 
  a 
  

   chalk-pit 
  on 
  the 
  roadside 
  ; 
  but 
  in 
  the 
  volume 
  devoted 
  to 
  the 
  Upper 
  

   Chalk 
  mention 
  is 
  made 
  of 
  the 
  large 
  quarries 
  south 
  of 
  Ofiham 
  ; 
  these 
  

   are 
  stated 
  (vol. 
  iii, 
  p. 
  46) 
  to 
  "exhibit 
  a 
  fine 
  section 
  through 
  the 
  

   zones 
  of 
  JlJicraster 
  cortestndinarinm 
  and 
  ILolader 
  flanus 
  into 
  the 
  

   Terehratulina 
  zone", 
  and 
  a 
  measured 
  section 
  of 
  the 
  quarries 
  is 
  given. 
  

   It 
  is 
  also 
  recorded 
  in 
  the 
  same 
  work 
  (p. 
  47) 
  that 
  "The 
  highest 
  part 
  

   of 
  the 
  zone 
  of 
  31. 
  cortestudinariuvi 
  appears 
  to 
  be 
  exposed 
  in 
  the 
  

   upper 
  pit 
  on 
  OfFham 
  Hill 
  now 
  disused 
  ". 
  There 
  is 
  no 
  record 
  of 
  any 
  

   pit 
  to 
  the 
  north 
  of 
  Off 
  ham. 
  

  

  In 
  1827 
  J. 
  de 
  C. 
  Sowerby^ 
  figured 
  an 
  example 
  which 
  he 
  referred 
  

   to 
  Mantell's 
  species, 
  and 
  characterized 
  the 
  species 
  as 
  follows 
  : 
  

   " 
  Umbilicated, 
  costated 
  ; 
  costee 
  large, 
  numerous, 
  annular, 
  simple; 
  

   whorls 
  ventricose, 
  very 
  few 
  ; 
  the 
  inner 
  ones 
  half 
  exposed; 
  apertuie 
  

   transverselj' 
  oblong." 
  

  

  ^ 
  The 
  Survey 
  include 
  in 
  the 
  Lower 
  Chalk 
  the 
  zone 
  of 
  Schlcenbachia 
  varians 
  

   and 
  the 
  zone 
  of 
  Holaster 
  subglobosus 
  (having 
  at 
  its 
  top 
  the 
  marls 
  with 
  

   Actinoc'amax 
  x)Jenus, 
  that 
  are 
  regarded 
  as 
  constituting 
  a 
  subzone). 
  

  

  2 
  J. 
  de 
  C. 
  Sowerby, 
  Min. 
  Conch., 
  vol. 
  vi, 
  1827, 
  p. 
  105, 
  pi. 
  DJv, 
  fig. 
  '2. 
  

  

  